Kale – A Top Source of Beta-Carotene
When we think of beta-carotene, we usually conjure up images of carrots and other orange vegetables. But did you know that this yellow-orange carotenoid is also abundant in a number of other vegetables? Kale, for example, is packed with beta-carotene, although in this green leafy vegetable beta-carotene is masked by the presence chlorophyll, a green pigment. In fact, according to data published by the U.S. Department of Agriculture (USDA), just 100 grams (or 3.5 ounces) of raw kale delivers a whopping 5.9 milligrams of beta-carotene, which corresponds to about 70% of the amount of beta-carotene found in a 100-gram serving of raw carrots. As heat reduces the water content of vegetables, cooked kale contains even more beta-carotene on a weight-for-weight basis: about 8.2 milligrams per 100 grams.
But it's not just the amount of beta-carotene that counts. If your body cannot absorb the beta-carotene in your digestive system, this carotenoid won't be of much use.
There are a number of factors that influence how much, or little, of the absolute amount of beta-carotene found in a specific food your body will absorb. To learn how to get the most beta-carotene out of your kale-containing dishes, keep reading.
Cooking Improves Beta-Carotene Release
Compared with many other nutrients, beta-carotene is relatively heat stable, meaning that it is not easily destroyed by cooking. In fact, research suggests that cooking can actually enhance the carotenoid release from vegetables by softening or breaking down their cell walls, thereby improving the bioavailability of beta-carotene (in case you are not familiar with the term, bioavailability simply refers to the body's ability to absorb and use nutrients like beta-carotene). But when it comes to cooking kale, there are also some tradeoffs. While cooking improves the bioavailability of beta-carotene, it can destroy a significant amount of heat-sensitive nutrients and phytochemicals. For example, in one study, researchers from the University of Agriculture in Krakow, Poland, found that cooking kale resulted in a 89% loss in its vitamin C content and a 56% loss in its polyphenol content.
Dietary Fat Enhances Beta-Carotene Absorption in Your Body
Whether you like your kale raw or cooked, be sure to include some healthy fats when you cook or eat kale. Beta-carotene is a fat-soluble nutrient, which means it is best absorbed from food when also some fat is present in a meal. But you don't need much fat for that: a study published in The American Journal of Clinical Nutrition in September 1998 suggests that as little as 3 to 5 grams of fat per meal is enough to boost the carotenoid absorption from foods. That's about the amount of fat found in a teaspoon of olive oil!
Chopping, Liquefying and Pureeing Also Improve Beta-Carotene Release
In raw vegetables, beta-carotene is embedded in a matrix with protein. If this matrix is not broken down, the beta-carotene is not released and your body will only absorb a small percentage of the total amount of the beta-carotene present in your meal. As explained above, cooking helps disrupt the matrix, but also chopping, liquefying and pureeing have been shown to improve beta-carotene release from green leafy vegetables. A study published in the February 1999 issue of The Journal of Nutrition, for example, found that beta-carotene in spinach leaves was more bioavailable when the leaves were minced or liquefied before consumption. Now that sounds like a pretty good reason to get one of those masticating juicers designed for leafy veggies such as kale or spinach, or to add some fresh kale into the blender next time you are making a fruit smoothie!
Dehydrated Kale Products – A Concentrated Source of Beta-Carotene
When fresh kale is out of season, freeze-dried kale powder and other dried kale products such as kale chips are a good alternative. When kale leaves are dried, their water content is reduced close to zero. This makes dried kale leaves an extremely concentrated source of nutrients (even though leaf for leaf, they contain fewer nutrients than their fresh counterparts). A study published in the August 2013 issue of the Journal of Food Processing and Preservation, for example, found that a 100-gram serving of air-dried kale leaves contained a whopping 158 milligrams of carotenoids. And, compared with air-dried leaves, the average amount of carotenoids in freeze-dried kale leaves was even 9% higher.
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